A major push in telecommunications today is the ability to offer services in support of the telecommunications environment that are not directly involved in call control functions. These services include, for example, geographic routing of centrally dialed calls to a branch location nearest the caller and voice activated dialing (VAD).
The architectural groundwork for these services was laid with the deployment of the Integrated Services Digital Network (ISDN) protocol for digital data transmission between network elements, as generally described in Bell Communications Research publication TR-NWT-001268, "ISDN Primary Rate Interface Call Control Switching and Signaling Generic Requirements," Issue 1, Rev. 2, March 1994, Morristown, N.J., the ISUP protocol for interworking communications between ISDN networks, as generally described in American National Standards Institute (ANSI) standard T1.113-1995, "Signalling System Number 7 (SS7)--Integrated Services Digital Network (ISDN) User Part," 1995, New York, N.Y., and the SS7 protocol which, inter alia, transports ISUP messages, and is generally described in ANSI publications T1.110-1992, "Signalling System No. 7 (SS7)--General Information," 1992, New York, N.Y., and the other standards in this series, T1.111-1992, T1.112-1988, T1.114-1996, T1.115-1996, T1.116-1990, and T1.118-1992.
ISDN is generally defined as a network that provides end-to-end digital connectivity to support a wide range of telecommunication services, including voice and non-voice services, to which users have access by a limited set of standard customer interfaces. ISDN is implemented on the existing public switched telephone network (PSTN) to carry a digital signal instead of the conventional analog voice signal. Access to the ISDN network is through one of two defined access interfaces: the basic rate interface (BRI) and the primary rate interface (PRI). With BRI, the digital information is transmitted over three multiplexed channels: two 64 kilobits per second (kbps) bearer channels ("B" channels) are provided for voice or data connections, and one 16 kbps signaling channel ("D" channel) is provided for exchanging control information between user and network. In PRI, there are 24 multiplexed channels: 23 B channels and one D channel. Control information exchanged on the D channel includes call set-up transactions necessary to establish a connection on a B channel. Implementation of ISDN requires upgrades to central office switching and transmission equipment at a minimum, with full implementation also requiring special user terminal equipment.
The communications protocol for the ISDN network is designed as a structured set of protocols which form a hierarchy. Each protocol of the hierarchy is referred to as a "layer" and each layer is dedicated to a specific function or a set of functions. Of particular interest to the present invention is the protocol governing the network layer (layer 3) of the D channel protocol. Specific functions performed by layer 3 include: processing of primitives for communicating with the data link layer, administration of timers and logical entities used in call control procedures, and administration of access resources including B channels. The following general functions may also be performed by layer 3: routing and relaying of messages, network connections, network connection multiplexing, segmenting and blocking of long messages, error detection, error recovery, sequencing, and flow control.
Layer 3 of the D channel protocol is defined in International Telecommunication Union--Telecommunication Standardization Sector (ITU-T) standards publication ITU-T Q.931, "Digital Subscriber Signalling System No. 1 (DSS 1)--ISDN User-Network Interface Layer 3 Specification for Basic Call Control," March 1993, which is hereby incorporated by reference.
ISDN has enabled the implementation of many useful features based primarily on the ability of ISDN to deliver the calling party's directory number to the called party.
A market push for more complex enhanced services offerings has led to the development of the Advanced Intelligent Network (AIN) protocol, as described in Bell Communications Research publication GR-1129-CORE, "Advanced Intelligent Network (AIN) 0.2 Switch--Intelligent Peripheral Interface (IPI) Generic Requirements," December 1995, Issue 1, Rev. 2. AIN provides for a large set of services to the customer and allows the telephone, data and signaling networks to easily adapt to technological advances. The AIN architecture encompasses programmable, reusable functionality for network systems (service control points, adjuncts, and intelligent peripherals), network elements (AIN service switching points, non-AIN switching systems, network access points, and signal transfer points) and operating systems. A primary feature of AIN is the use of software "triggers" on AIN-provisioned switches. Trigger criteria are used to define when a call requires special handling. When a defined set of trigger criteria are satisfied, the trigger logic of the switch suspends call processing, sends a service query message to a service control point (SCP) to request information on how to handle the call. Upon receiving a response message from the SCP that includes call routing information, the switch resumes call processing and routes the call as indicated in the response message. The major service drivers for AIN were Personal Communications Services (PCS) network access services and VAD. However, AIN architecture is not limited in any respect to these two applications. Full implementation of AIN also requires upgrades to central office switching and other network and transmission equipment.
In today's telecommunication network, ISDN is deployed in almost all major metropolitan areas with some deployment throughout the rest of the PSTN network. AIN does not share a similarly wide deployment. This presents a problem in satisfying customer demands for enhanced services that are geared to AIN.
Accordingly, it is an object of the present invention to provide a method of implementing AIN-like services in an ISDN network.